The present invention relates in general to energy absorbers to reduce the influence of externally induced motion on structures, and more particularly to a load bearing assembly for mounting between a foundation and a structure to protect the structure from undesirable effects associated with an earthquake.
The earthquake phenomenon presents kinetic energy in a low frequency oscillatory mode. The part of the earth's surface directly above the focus of an earthquake is referred to as an epicenter. Kinetic energy resulting from an earthquake travels outward from the epicenter, effecting movement of the ground in its path. For purposes of analysis, the kinetic energy may be considered as being comprised of horizontal and vertical components. In practice, the horizontal components are typically of a greater magnitude than the vertical components.
Building constructions have the foundations thereof rigidly fixed to the ground. As a consequence thereof, energy present in an earthquake is transmitted to the building foundation, and, hence, to the building itself, resulting in structural failure. Foundations have been employed to limit the magnitude of the force transmitted to a building during earthquakes.
In U.S. Pat. No. 3,748,800, issued on July 31, 1973, to Raymond C. Glicksberg, for Earthquake-Insulation Foundations, there is disclosed a watertight building-base located within a water filled pool excavated in the earth, having sides and a bottom which are flexibly reinforced. The base of the building is centrally positioned within the pool by means of centering springs which provide a return force between the sides of the pool excavation and the sides of the base. Also disclosed in U.S. Pat. No. 3,748,800 is a flat bottomed building-base that rests on a surface of a pit of sand or other dry granular material.
In U.S. Pat. No. 3,906,689, issued on Sept. 23, 1975, to Tadayoshi Nakayama, for Apparatus For Absorbing Or Damping Vibrations Of The Ground, there is disclosed an apparatus for absorbing or damping vibrations of the ground caused by earthquakes and the like before the vibrations are transmitted to a building. The apparatus comprises a main vibration absorbing assembly and an auxiliary load carrying assembly, which are individually disposed between a groundsill of the building and the foundation of the building. The main vibration absorbing assembly comprises a group of springs mounted on a plate, with the axes thereof being inclined upwardly and inwardly so as to converge at an intersecting point where they are pivotally connected for tilting movement in every direction. The auxiliary load carrying assembly comprises a frame mounted under groundsills in positions directly under struts of a building, and an associated ball supported at the lower end of the load carrying assembly, in rolling engagement with the foundation.
U.S. Pat. No. 4,166,344, issued on Sept. 4, 1979, to Aristarchos S. Ikonomou, for Earthquake Guarding System, discloses a support and connecting means. The support provides elastic resistance to the movement of an associated structure and the connecting means provides a frangible link between the structure and the ground, breaking when the forces associated with an earthquake exceed a predetermined strength.
U.S. Pat. No. 4,533,109, issued on Aug. 6, 1985, to Heinz Delam, for Elastic Support Unit, discloses the use of an elastic support unit having a supporting element. The supporting element includes an elastic part and a sliding part. The elastic part is first elastically deformed under the action of a load and the supporting element acts within a first region. Then, the sliding part allows the supporting element to slide over a slide path and the supporting element acts within a second region. Thereafter, the supporting element upon passing the sliding region uses its stress reserve and after exceeding the stress reserve deforms the elastic part and thereby acts in a third region.
U.S. Pat. No. 4,121,393 issued on Oct. 24, 1978 to Jean Renault, et al., for Device For Protecting A Structure Against The Effects of High Horizontal Dynamic Stresses, discloses a system of friction supports comprised of seating blocks applied against each other and incorporated respectively with a structure and a foundation. Relative displacement is permitted employing friction of the associated seating blocks along their mutual bearing interface.
U.S. Pat. No. 4,527,365, issued on July 9, 1985, to Toshikazu Yoshizawa, et al., for Earthquake Insulating Bearing Assembly, discloses a first and second friction member employed in an elastic bearing assembly. Corrective action with respect to the bearing assembly subsequent to an earthquake is employed with respect to the second friction member. Also disclosed as prior art in this patent are several types of elastomeric bearings including metal sheets interspersed between layers or sheets of an elastic material. U.S. Pat. No. 4,499,694, issued on Feb. 19, 1985 to Ian G. Buckle, et al., for Cyclic Shear Energy Absorber, discloses a cyclic shear energy absorber to absorb energy induced by motion between members by plastic cyclical deformation of a central energy absorber core. The core is surrounded by a restraining element having movable inner walls. The restraining element is confined to a cylindrical aperture formed in a resilient support. The resilient support has alternate layers of a resilient material and stiffener plates. The resilient support functions as a bearing pad for transferring vertical loads through the device.
U.S. Pat. No. 4,187,573, issued on Feb. 12, 1980, to Edward R. Fyfe, et al., for High Load Bearing For Bridges And Similar Structures, discloses an elastomer pad having a concave periphery and means which mechanically abut the elastomer pad to limit lateral movement on the upper and lower surfaces of the elastomer pad. U.S. Pat. No. 4,514,942, issued on May 7, 1985, to Adrian Pocanschi, for Damping Installation For Earthquake-endangered Buildings, discloses a vibration insulator between a foundation and a building.
U.S. Pat. No. 3,921,240, issued on Nov. 25, 1975 to Edward R. Fyfe for Structural Bearings discloses a stuctural bearing, such as employed in bridges and large buildings, comprising a relatively thin layer of an elastomer interposed between and bonded to two flat bearing members, with at least one shear-resisting member extending between the two flat bearing members and being in shear-resisting pivotal engagement with one of them so as to accommodate vertical compression of the elastomer and tilting of the two flat bearing members. The structural bearings disclosed in this patent for use in bridges and high buildings also have features enabling them to accommodate sliding movement between the foundation and the structure supported by it.
U.S. Pat. No. 4,718,206, issued on Jan. 12, 1988, to Edward R. Fyfe, et al., for Apparatus For Limiting The Effect Of Vibrations Between A Structure And Its Foundation, discloses an elastomeric bearing pad and a hollow member disposed between the structure and its foundation. A cable or tensioning device, anchored at one end to the foundation, is centrally disposed within the elastomeric bearing, extending into the hollow chamber, and has a stop on the free end within the hollow chamber. The stop serves to limit horizontal and vertical movement of the elastomeric bearing.